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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 90 |
| 4 | 2520 |
| 5 | 113400 |
| 6 | 7484400 |
| 7 | 681080400 |
| 8 | 81729648000 |
| 9 | 12504636144000 |
| 10 | 2375880867360000 |
| 11 | 548828480360160000 |
| 12 | 151476660579404160000 |
| 13 | 49229914688306352000000 |
| 14 | 18608907752179801056000000 |
| 15 | 8094874872198213459360000000 |
| 16 | 4015057936610313875842560000000 |
[1,1,6,90,2520,113400,7484400,681080400, 81729648000,12504636144000,2375880867360000, 548828480360160000,151476660579404160000, 49229914688306352000000, 18608907752179801056000000, 8094874872198213459360000000, 4015057936610313875842560000000] |